The invention relates to self-locking hydrostatic differential gearing for the distribution of an input torque to two driven shafts with an incorporated locking mechanism of the type having an input shaft which drives a first gear component in which spur-toothed compensating gears having parallel axes of rotation are rotatably housed, of which at least two respectively mesh with one another, and operate as geared pumps with enclosed operating medium, with one pinion being in engagement with a second gearing component and the other pinion being in engagement with a third gearing component, the axis of rotation of which and also the axis of rotation of the second gearing component extending parallel to the axis of rotation of the compensating gears which are enclosed as far as possible by the first gearing component and between this have sealing clearances to achieve the throttling effect, with, when viewed in circumferential direction, respectively two adjacent pinions which do not mesh with one another, being in engagement with the same gearing component and having the following further features:
a) in the region of the toothing the circumference of the pinions is as wide as possible and the front sides of the second and third gearing components are tightly enclosed for formation tip clearance conduits and lateral clearance conduits;
b) each pinion comprises just a single toothing geometry with additional pressure zones being formed in the common region of engagement of two meshing pinions of a pinion pair;
c) with the assistance of a casing the first gearing component is fluid-tight with respect to the interior of the differential gear housing in which a drive gear attached to the first gearing component rotates.
Differential gearings of this type are used in particular in vehicle drives to distribute the drive torque to the wheels on each side or to several axes of the vehicle.
As known, the purpose of locking mechanisms on differentials is to ensure that, at least on one driven side of the differential, i.e. the wheel on one side of the vehicle retains a large part of its torque if, on the other side of the differential, i.e. the wheel on the other side of the vehicle does not transmit a torque. For this purpose from German Patent Specification 35 42 184 apparatus is known with which in an epicyclic differential gearing the epicyclic gears form geared pumps with the sun wheel and the annular gear wheel. For this purpose all clearances on the front sides and on the tip surfaces are constructed as parallel sealing clearances and are dimensioned in such a way that a build-up of pressure is produced by throttling the leakage return flow. This build-up of pressure is a standard for the locking moment between the two driven sides of the differential gearing. However in the disclosed development the known differential gearing can not develop any drive or locking moment of the same level on the two driven sides. Moreover, the maximum locking moment developed is relatively small, in particular for applications where no transmission stage increasing the drive or locking moment is provided behind the two driven shafts.
To increase and simultaneously to divide the locking and output torque uniformly over the two driven sides of the differential gearing, it has been proposed in Applicants earlier German Patent Application P 38 10 169.6-12 to construct the differential gearing just as a spur gear differential. The two driven shafts support spur gears of equal size, which are mutually connected by means of pinions disposed in pairs in such a way that the effect of geared pumps is again produced. Each pinion of a pinion pair meshes both with one of the two spur gears and also with the other adjacent pinion. To obtain a number of pressure zones which is as large as possible and consequently the largest possible locking moment, an equal number of pinion pairs is provided. The arrangement in the circumferential direction is selected so that two adjacent and not mutally meshing pinions are in engagement with the same driven spur gear. This alternating arrangement of the pinion pairs over the circumference of the spur gears achieves a significant increase in the locking moment, but this is still not adequate for many applications.